Thyroid hormones (TH) play an integral role in neuro-development, particularly in the maturation of the corpus callosum, cerebellum, hippocampus, and inner ear. In rodents, it has been shown that persistent organic pollutants (POPs), particularly polychlorinated biphenyls (PCBs), interfere with TH signaling. These pollutants are widespread in the marine environment and biomagnify in marine mammals to very high levels. Brominated flame-retardants have also recently been shown to interfere with the TH system in experimental animals.